Single Stage coil gun

[windozeuser]

Hey, I currently got into the mood to build a coil gun :twisted:. I've been thinking of buying some photo flash capacitors about 15, 150uF caps. Wiring them in parallel, and using the charger circuit from a throw-away camera. The barrel will probably be a disassembled pen with magnet wire wrapped around it.

I was thinking about using these capacitors:
https://www.electro-tech-online.com/custompdfs/2005/11/e_FK.pdf

Please if you know of better ones, please post.

Some questions I have are, where can I buy photo capacitors cheaply? How do I calculate the amount of energy the capacitors will release, and be sure the wire can handle the current? Also, what can I build to charge the capacitors effciently.

I'm open to suggestions, please share your experiences and ideas.

Thanks!

Note: I only want to build a Single Stage coil gun, I will be happy if it can accelerate a projectile about 35 feet

 

[DigiTan]

amazing1.com sells a very similar capacitor for $12.95 each. I've managed to get this type of capacitor for as low as $10 each in the surplus market, but this was a walk-in store and is a pretty tough price to beat. I've also gotten discarded cameras from Walgreens and CVS pharmacy. If they ask why, just say you want the capacitor--you'll get a free battery too.

The total energy storage is calculated by:

E = 0.5*(C*V²) [ in Joules]

...this is still misleading because your capacitor won't be able to discharge all that energy before the projectile leaves the barrel. Typical homemade coilguns only convert about 1% or 2% of their energy bank into motion; and Los Alamos was up to the 20%'s--probably thanks to superconductors.

One device you might like is the Marx Generator. It charges your capacitors in parallel and discharges them in series. That (tends to) drive charge through the coil faster, resulting in a more violent launch.

Anyway, there are alot of other factors to throw in like coil saturation (heating), projectile saturation, switching, etc. My best advice is to start things by designing and testing the coil, then choosing the projectile. There's a listing of 15 Real Coilguns on the link; a few are even uC-controlled. 8)

 

[audioguru]

I think you need a real capacitor charger. The little thing in a camera will melt before it takes a very long time to charge all your paralleled caps.

 

[George L.]

Hello windozeuser,

Insead of spending a lot of cash for some photoflash caps, you should just got to a few places and get them for free like Digitan said, I did this and got about 20 from walmart in one trip. (Don't get shocked when taking them out of the cameras, some are charged when you get them (PAINFUL)!

You could probably make a simple circuit to charge the caps faster than the camera circuit does. To chareg a 10 cap bank it takes more than a minute!. A 555IC, the transformers in the cameras and a few resistors should charge them up very quickly.

George L.

 

[williB]

windozeuser
Have you tred eBay, lately i've seen some pretty powerfull caps on ebay , they are used for car audio sound systems..
two or three of the single Farad versions in parallel , could probably start your car, or shoot a neo magnet through the wall :twisted: ..

 

[Someone Electro]

You need an much higer voltage than 12V.

I found out 50V not enugh.So i went to 100V.Most coilguns work from 400 to 800V.

 

[audioguru]

Somebody on one of these posts is claiming a coil current of 500A through his little wires with alligator clips!
I think the little wire would jump farther than the projectile if it had as much as 10A through it.

 

[Nigel Goodwin]

Somebody on one of these posts is claiming a coil current of 500A through his little wires with alligator clips!
I think the little wire would jump farther than the projectile if it had as much as 10A through it.

Yes, there's some very imaginative values about! :lol:

 

[windozeuser]

Hey thanks for all your replies

Hello windozeuser,

Insead of spending a lot of cash for some photoflash caps, you should just got to a few places and get them for free like Digitan said, I did this and got about 20 from walmart in one trip. (Don't get shocked when taking them out of the cameras, some are charged when you get them (PAINFUL)!

I went to wallmart today and asked the lady in the photo department "Do you resell or give away throw-away cameras you develop" Shes like "NO, We recycle our throw-away cameras, it's not in my policy to give you any"


How did you guys get them?

Btw, I bought 40 feet of 22 gauge magnet wire from radioShack. Is there a guide on how to construct coils around say a certain diameter tubing. Then find out the strength of the flux lines inside the tubing.


Thanks a lot

Somebody on one of these posts is claiming a coil current of 500A through his little wires with alligator clips!
I think the little wire would jump farther than the projectile if it had as much as 10A through it.

Wouldn't the entire current just be a huge spike that only last a couple of mS's? Would that be enough to heat the coils up and cause them to short out and arc? I guess it would depend on the inductance of the coil with and without the ferrous projectile, and also the resistance of the coil?

But as I see the power value of a theoretical 400V setup...

P= 500A * 400V = 200,000 Watts o.o

How do you calculate the current capacity of magnet wire?

windozeuser
Have you tred eBay, lately i've seen some pretty powerfull caps on ebay , they are used for car audio sound systems..
two or three of the single Farad versions in parallel , could probably start your car, or shoot a neo magnet through the wall :twisted: ..

Or knock you dead cold in less than a second heh heh, but seriously thanks for the advice I'm gonna search ebay right now

 

[audioguru]

The high-current pulse is so quick that only little wires with alligator clips would get hot and maybe melt. I think the little wires are 22 guage like the wimpy wire you bought.
If you made the circuit into a rapid fire machine gun then lotsa stuff would get hot. :lol:

 

[audioguru]

Oh yeah, forget about the low voltage caps for car amps. You need high voltage to produce enough current in the coil.

 

[windozeuser]

What do you think about buying say uninsulated 14 or 12 gauge copper wire, then coating it in my own enamel? Instead of using that 22 gauge floss ;P

I would think it would open up a wide range of potential failure, and also what would I use to coat the wires if I can't obtain enamel?

 

[DigiTan]

I went to wallmart today and asked the lady in the photo department "Do you resell or give away throw-away cameras you develop" Shes like "NO, We recycle our throw-away cameras, it's not in my policy to give you any"

How did you guys get them?

Basically, I waltzed into Walgreens, and asked what they did with cameras they were throwing out. The photo guy asked if I had lost film, and just said I needed the transformer--and they pulled it out of the bin. If they ask questions, make it clear you're not interested in film, you're just a student/hobbyist/professional in need of the components.

Like the others suggested, I wouldn't recommend using the camera's supply. It uses a cheap load-dependent oscillator for DC-to-DC, and even cheaper step-up transformers. A high-end gun would also use NiCad, Nickel-Metal, or --in the extreme-- LiPoly batteries for a source.

The single-stage designs seem of favor the heavy guages.

 

[audioguru]

What do you think about buying say uninsulated 14 or 12 gauge copper wire, then coating it in my own enamel? Instead of using that 22 gauge floss?

RadioShack isn't the only electronics parts supplier. Digikey and Newarkinone have thousands of enamel-coated wire sizes and lengths and if you place an order before 8:00PM, it is delivered to you the next morning at much less cost than RadioShack.

22 guage wire will hug the coil former closer and would be fine with a few hundreds of volts supply for the pulse.

 

[Roff]

I'm planning on ordering magnet (enameled) wire from . They have really good prices if you need a couple pounds or more of one size wire.

 

[williB]

I'm planning on ordering magnet (enameled) wire from . They have really good prices if you need a couple pounds or more of one size wire.

a while back , i bought 10 lbs of 20 gage for $39 + shipping..about $ 45 total..ebay

 

[windozeuser]

Can anyone help me with the charger circuit for the caps? I want it to operate on possibly a 9 volt battery, then step it up to about 300 volts.

 

[windozeuser]

I was snopping around my parts room and came across two

General Electric 86F142M

32,000 uF -10+75%

25 VDC 30 surge Capacitors, Is there any way I could impletement those even with the low voltage?

I'm about to salvage some old computer monitors

 

[troymacdonald]

I recently got into this hobby myself and built a prototype coil gun by moding (or hacking, depending on your preferred terminology) a Nerf N-Strike. I used three disposable camera charger circuits (Walgreens was kind enough to give me a box of about 30 for free) connected in parallel with the output going to three 400V - again connected in parallel to get a combined ideal output of 1200V over a 8 layer 23awg coil.
Now my multimeter only reads up to 1000V so I can't be sure if the caps charged completely, but it did fling a cut nail across my garage. I agree with other posts that the charger circuits I used are incredibly inefficient and take a long time to charge, so making a full auto coil gun is mostly out of the question with this method.

If you google DC-to-DC step up converter, or high voltage DC power supplies you will find several good schematics for circuits you can use that will be somewhat more efficient.

I've collected a lot electronics parts to make some of these circuits and plan on making a multistage coil rifle firing a 100gram steel (not stainless) target archery tip.

In my hunt for research material for this I came across a 1999 paper from Polytech University in Brooklyn where their Electronical Engineering department built and tested a coil gun based on a military Mark 19 grenade launcher tube and projectile. They were able to get velocities of 241m/s and 700m/s respectively. I'm hoping to eventually make one that has velocity within that range.

I am curious as to wether using a standard DC up converter would be better versus a Marx generator.

My work area is mostly designed for wood working, but I suspect through the course of this project I'll eventually have a full blown electronics lab with magnometer (sp?), oscillioscope and other cool little expensive gadgets.